Coffeelake and Kabylake LGA1151 pins are different

Intel added more VSS (ground) and VCC (power) pins for 8th Gen CPUs. This was not really mentioned by Intel during the press call, but apparently, the pin layout is now available explaining why it was necessary to exclude Kabylake CPUs from the support list on Z370 motherboards.

VSS: 377 -> 391 (+14)

VCC: 128 -> 146 (+18)

RSVD: 46 ->25

According to Intel, LGA1151 socket on Z370 motherboards had to be modified for better power delivery for 8th Gen Core CPUs. The backward and forward compatibility questions could’ve all been avoided if Intel added at least one more physical pin or simply name the new socket as LGA1151v2. That did not happen. The electrical pin layout confirms that Coffelake has some RSVD (reserved) LGA1151 pins now occupied by VSS and VCC pins.